1. Field of the Invention
This invention relates to a shutter which is installed in a doorway or window.
2. Description of the Prior Art
As shutter elevating means two types are well known; in one type slats are wound up by the use of the urging force of a spring accommodated inside a take-up shaft and in the other type the slats are wound up by turning the take-up shaft manually or by the use of a motor. According to the shutter of the type in that it is elevated by turning the take-up shaft manually or by the motor, the slats are mutually coupled vertically expandably, slits are formed which are exposed only when the slats are in the expanded state, and lighting and draft are effected if the slits are exposed even when the slats have been unwound.
On the contrary, in the shutter of the type in that it is elevated by the use of the urging force of the spring, because it is difficult to finely control rotation of the take-up shaft, the slats are coupled without an expandable function and no slit is formed. Accordingly, this type does not permit lighting and draft in the unwound state of the shutter.